Friction welding (FW) is a process of joining two components which may be made from the same or different materials. The FW process typically involves pressing one of the two components against the other component with a large amount of force and rapidly moving one of the two components with respect to the other component to generate friction at the interface of the two components. The pressure and movement generate sufficient heat to cause the components to begin to plasticize. Once the two components are plasticized at the contact interface, the relative movement of the two components is terminated and an increased force is applied. As the components cool in this static condition, a weld is formed at the contact interface.
The weld obtained using FW is a solid state bond which is highly repeatable and easily verifiable. For example, the amount of material donated by each component to the formation of the weld, which is referred to as “upset”, is well defined. Therefore, by carefully controlling the energy input into the FW system in the form of friction and forging pressure, the measured upset of a welded assembly provides verification as to the nature of the weld obtained.
As discussed above, relative movement of the two components is a critical facet of FW. Different approaches have been developed to provide the required relative movement. One widely used approach is rotational friction welding (RFW). RFW involves rotation of one component about a weld axis. RFW provides many benefits and is thus a favored welding approach in various industries including aerospace and energy industries.
RFW, however, does have some limitations. For example, in forming a weld, the interface between the two components must be evenly heated to generate a uniform plasticity within each of the components throughout the weld interface. If one area becomes hotter than another area, the material in that hotter area will be softer, resulting in an incongruity in the formed weld. To provide consistent heat generation throughout the component interface, the rotated component is necessarily uniformly shaped about the axis of rotation, i.e., circular. Moreover, since the heat generated is a function of the relative speed between the two materials, more heat will be generated toward the periphery of the rotated component since the relative speed at the periphery is higher than the relative speed at the rotational axis.
In response to the limitations of RFW, linear friction welding (LFW) was developed. In LFW, the relative movement is modified from a rotational movement to a vibratory movement along a welding axis. By controlling the amplitude and the frequency of the linear movement, the heat generated at the component interface can be controlled.
LFW thus allows for welding of a component that exhibits substantially uniform width. LFW, like RFW, is subject to various limitations. One such limitation is that LFW exhibits non-uniform heating along the welding axis due to the linear movement of the vibrated component. For example, when welding two components of identical length along the welding axis, the two components are aligned in the desired as-welded position. Due to the nature of previous LFW systems, this location corresponds to the rearmost position of the component which is moved. The leading edge of the vibrated component is then moved beyond the corresponding edge of the stationary component by a distance equal to the amplitude of the vibration. Moreover, the trailing edge of the vibrated component exposes a portion of the stationary component as the leading edge of the vibrated component moves beyond the corresponding edge of the stationary component. Accordingly, the portion of the vibrating component that moves beyond the corresponding edge of the stationary component and the exposed portion of the stationary component will not be heated at the same rate as the remaining surfaces at the component interface. Therefore, manufacturing process must take the incongruity of the welds into account such as by machining off a portion of the welded components at the leading edge and the trailing edge of the formed weld.
Moreover, in order to achieve the frequency and amplitude necessary to realize a weld, a LFW device must provide for rapid acceleration from a dead stop. The moving component must then be completely stopped and reaccelerated in a reverse direction. As the size of the vibrated component increases, the momentum that must be controlled becomes problematic. Thus, traditional LFW devices incorporate massive components which are very expensive.
A related limitation of LFW processes is that the relative motion between the two components must be terminated in order for the weld to form properly. Merely removing the motive force does not remove the momentum of the vibrated component. Additionally, any “rebound” or damped vibrations of the moving component as it is immobilized weakens the final weld since the plasticized metals begin to cool as soon as the vibrating movement is reduced.
One approach to solving the need to rapidly immobilize the moving component is to jam the motion-inducing system such as by forcibly inserting a device into the motion inducing system. Freezing the system in this fashion can provide the desired stopping time. This approach, however, results in significant forces being transmitted through the system, necessitating oversized components to be able to withstand the shock. Moreover, the exact position of the vibrated component with respect to the stationary component is not known. Therefore, manufacturing processes must account for a possible position error potentially equal to the amplitude of vibration.
Therefore, a LFW system and method which provides consistent welds is beneficial. A LFW system and method which allows for smaller components within the system would be beneficial. A LFW system and method which reduce the errors associated with the LFW process would be further beneficial.